BIAS IN QUADRAT-DERIVED ESTIMATES OF NUMBER OF PRAIRIE WETLANDS

Estimates of number of wetlands derived from quadrat sampling are inhe rently biased when wetlands on quadrat boundaries are counted. Bias co mplicates comparisons of wetland density or abundance between years or studies, or between regions with different wetland sizes. Simulated q uadrat sampling was conducted to evaluate the magnitude of bias in est imates of the number of temporary, seasonal, semipermanent, and total wetlands from samples of square quadrats of different sizes. All estim ates were biased except for number of temporary wetlands derived from samples of the largest quadrats. Bias ranged from + 101% (SE = 0.39%) for estimates of the number of semipermanent wetlands sampled with 0.6 4 km(2) quadrats to + 0.19% (SE = 0.19%) for the number of temporary w etlands sampled with 25.60 km(2) quadrats. Bias was greatest when larg e wetlands were sampled using small quadrats and was related to quadra t perimeter:area ratio (km/km(2)) and to quadrat size. Managers and re searchers should correct for bias in estimates of number of wetlands b y deriving correction factors with the equations presented or by deriv ing correction factors using aerial photographs to determine the geome tric centers of wetlands in and around a subset of sample quadrats.